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<li class="toctree-l1"><a class="reference internal" href="Section_modify.html">10. Modifying &amp; extending LAMMPS</a></li>
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<div class="section" id="fix-modify-command">
<span id="index-0"></span><h1>fix_modify command<a class="headerlink" href="#fix-modify-command" title="Permalink to this headline"></a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>fix_modify fix-ID keyword value ...
</pre></div>
</div>
<ul class="simple">
<li>fix-ID = ID of the fix to modify</li>
<li>one or more keyword/value pairs may be appended</li>
<li>keyword = <em>temp</em> or <em>press</em> or <em>energy</em></li>
</ul>
<pre class="literal-block">
<em>temp</em> value = compute ID that calculates a temperature
<em>press</em> value = compute ID that calculates a pressure
<em>energy</em> value = <em>yes</em> or <em>no</em>
</pre>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>fix_modify 3 temp myTemp press myPress
fix_modify 1 energy yes
</pre></div>
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</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>Modify one or more parameters of a previously defined fix. Only
specific fix styles support specific parameters. See the doc pages
for individual fix commands for info on which ones support which
fix_modify parameters.</p>
<p>The <em>temp</em> keyword is used to determine how a fix computes
temperature. The specified compute ID must have been previously
defined by the user via the <a class="reference internal" href="compute.html"><em>compute</em></a> command and it must
be a style of compute that calculates a temperature. All fixes that
compute temperatures define their own compute by default, as described
in their documentation. Thus this option allows the user to override
the default method for computing T.</p>
<p>The <em>press</em> keyword is used to determine how a fix computes pressure.
The specified compute ID must have been previously defined by the user
via the <a class="reference internal" href="compute.html"><em>compute</em></a> command and it must be a style of
compute that calculates a pressure. All fixes that compute pressures
define their own compute by default, as described in their
documentation. Thus this option allows the user to override the
default method for computing P.</p>
<p>For fixes that calculate a contribution to the potential energy of the
system, the <em>energy</em> keyword will include that contribution in
thermodynamic output of potential energy. See the
<a class="reference internal" href="thermo_style.html"><em>thermo_style</em></a> command for info on how potential
energy is output. The contribution by itself can be printed by using
the keyword f_ID in the thermo_style custom command, where ID is the
fix-ID of the appropriate fix. Note that you must use this setting
for a fix if you are using it when performing an <a class="reference internal" href="minimize.html"><em>energy minimization</em></a> and if you want the energy and forces it
produces to be part of the optimization criteria.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline"></a></h2>
<p><a class="reference internal" href="fix.html"><em>fix</em></a>, <a class="reference internal" href="compute_temp.html"><em>compute temp</em></a>, <a class="reference internal" href="compute_pressure.html"><em>compute pressure</em></a>, <a class="reference internal" href="thermo_style.html"><em>thermo_style</em></a></p>
</div>
<div class="section" id="default">
<h2>Default<a class="headerlink" href="#default" title="Permalink to this headline"></a></h2>
<p>The option defaults are temp = ID defined by fix, press = ID defined
by fix, energy = no.</p>
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